Electrical system



Jan. 18, 1949.

W. E. BRADLEY ELECTRICAL SYSTEM Filed March 25, 1946 INVENTOR. WILL/AME. BRADLEY WWW w QTW ATTORNEYS Patented Jan. 18, 1949 ELECTRIC L SYSTEMWilliam E; Bradley, Swarthmore, Pa., assignor, by .mesne assignments, toPhilco Corporation,

corporation of Pennsyl- Philadelphia, Pa., a

Vania Application March 26, 1946, Serial No. 657,175

invention relates in general to cathode ray tube scanning methods, andmore particularly concerns novel and simplified apparatus adaptable tocathode ray picture tubes for accomplishing keystone compensationlGenerally, in cathode ray television systems, scanning of a screen iseiiected by an electron beam within a cathode ray tube; Beam deflectionis-caused by horizontal and vertical sawtooth sweep voltages or magneticfields which Claims. v (01.250-157) tion ,vvas accomplished in a, numberof ways but in all cases it considerably complicated the sweep circuitsand added the need for critical adjustment to the system. Thesemodulating circuits resulted in additional stages, thus increasing cost1 and constituting an added source of failure.

ordinarily produce a rectangular raster of substantially horizontallines. In certain television pick-'up devices or cameras, as for examplethe icono'scope, the axis of*the cathode ray electron gun is at an angleto the screen surface being scanned. If then the scanning pattern isformed by horizontal and' vertical deflection voltages or fields havingconstant periods and amplitudes, the raster will not be rectangular.Thus, the horizontal scanning lines uppermost on the It has beendiscovered that the keystoning problem could be more convenientlyv andeconomically handled through the controlled distortion of the electronbeam movement by establishing a comparatively weak, continuous magneticfield through the cathode ray tube. Thus,

in co-pending application of' Fisher and John, SerialNo. 580,564, filedMarch 2, 1945 now abandoned and entitled Television system, it was shownthat the addition to the tube structure of ap'a'ir of small,-permanentmagnets, suitably screen, which are furthest from the electron gun,

will be longer than thelowermost horizontal lines, nearest the gun, withthe result that the scanning raster'is trapezoidal, or keystone, inshape. This trapezoidal efiect is highly undesirable in camera tubes.

In television projection type receivers, mechanical and opticalconsiderations often" dictate th at'the image presented upon the face ofa cathode ray'tube be projected upon'a viewing screen which is notnormal "to the optical axis ofproj'ection. If thefimage presented uponthe oathode ray tube were rectangular,-as would be the case where"uncompensated constantperiod and amplitude sweep voltages or fields areused, then the" picture appearing upon the viewing screen would bekeystoned in shape. I

{In both camera and projectionreceiver systems, the keystone effect is adistortion which must be eliminated. In the camera tube; a compensationmust'be made so thatthe actual-scanning raster is rectangularjwhereasin'the receiver tube mentioned, a keystone distortion-must be introducedto provide a trapezoidal cathode ray tube image which, in combinationwith the skew projection, produces a final image on the viewing screenwhichis rectangular, asdesired'.

' Heretofore, the introduction or the removal of akeystone effect hasbeen accomplished electrically' within' the sweep circuits; As anexample, it has been the practice to modulate the horizontal deflectionfvoltage with a predetermined component of the vertical sawtoothdefiectionvoltage, in that phase'which wouldprovidethe'propertrapezoidal effects This modulaoriented with respect tothe cathode ray tube electron beam, would produce or compensate forakeystone'raster. l i

There has, however, been a limitation on the extent of the use of thesystem disclosed in the aforementioned application, 'which results froma second distortion introduced, in addition to the keystone eifect.Thus, although the magnetic field formed a substantially trapezoidalraster, it also had the effect of bowing the horizontal scanning lines,such that a high degree of picture excellence was unattainable.

The present invention contemplates and, has as a primary object the;provision of simplified, inexpensive and non-critical apparatusadaptable to cathode ray tubes for accomplishing keystone compensationwithout theintroductionof other and undesirable distortion. Generally,the apparatus of this invention involves means for producing a pluralityof fixed and continuous magnetic fields which extend through a cathoderay tube and which are uitably disposed relativeto an electron beampassingtherethrough.

'It is another object of the present invention to provide magnetic meansfor producing a keystone eiiect in acathode ray tube which in itselfcauses substantially no displacement of the image center relative to thecenter of the screen.

A further object of this invention is to provide a simplified magneticstructure for producing the magnetic field required for keystonecorrection or trapezoidal correction of a scanning raster.

A still further object of the present invention is to provide asimplified magnetic structure for producing two magnetic fields within acathode ray tube, one ofsaid 'fields being substantially uniform and theother being distorted; in a, predetermined manner,

These and other objects of thepresent invention Will now become apparentfrom the following detailed specification taken in connection with theaccompanying drawings in which Figure 1 is a diagrammatic representationof a cathode ray tube and" illustratessthe' electron beamthereofrelative' to "the m aghetic fields established to provide akeystone effect;

Figure 2 is a front view of the screen of the:

cathode ray tube illustrated in Figure 1;,and.

Figures 3A, 3B, and 3C are a numbefo'fvi'ews' of a cathode ray tube and'atmagnetic structure for producing the particuIar 'fielclsillustrate'din Figure 1. i

Referring now to Figure 1, there is illustrated a conventionaltelevision receiverrcathode ray tube V II, having, as is well understoodin the art, an evacuatedglass envelope J2 and a plugin' tubebase I3.Within the glass structure I2 is an electron gun.- l *f-or igeneratingan electronibeam J 5i This electron gun: it. includes" at least aheatercathode conibination aacontro'l .gridfor determim ingaelectr'onbeamintensity and a number of accelerating? electrodes. 'iThe electron ibeam: 1 5 is directed tow'ard and impinges tupon ra fiuorescent soreencoating 1 l 6 :on thezinnerv surface: of the face ofz-glasssenv'elopef12. I

- .Inaorder'to" provide aisharply defined spot-on theiscreenI16;thezelectronzbeamiis focused 'thereon by a magnetic zfocusing; coil11-, slipped over the neck' of the glass envelope d2; its-illustrated,and

energized-byansadjustablecurrent from -a-source;

not shown; "The magneticifield ofithe'i focus-coirl l -issubstantiallyraxial-within. the tube, that is, parallel --to the?electron beams-l 5. Focusing may also'b'e accomplished:electrostatlcally by suitableelectrodes withinthaelectrongun structuret i.-

In television -apparatus, it -is necessary to sc-an. the fluorescentscreen with the electron-.beamd 5.-

This ;is\ generallyaocomplishedlby generatingtwc scanning-potentials;horizontal and vertical, and

appl-ying'these to mutuallyperpendicular deflecting means on the-cathoderay tube; -As illustrated in Figure 1, the deflec ing means comprise-,a,-mag netic defiection yol ze (2:1 .1 which-:is woundwith two coilshaving mutually perpendicular a Xes towhich;coilsrthedefiecting signalsare-applied:v The horizontal scannin signal frequency is apredeterminedmultipleflof-thevertical scannin signal frequencyso thatprdinarily asubstantially rectangular .raster. of .hor'izontal' lines obtained uponthe fluorescent screen" 161. 'It is clear. that:- the conventional" typeelectrostatic deflection cathode ray,Itube couldjbe .usedto provide thescanning raster instead' 'of' t'he magnetie deflection tubeillustrated vv a 1 b Aspreviouslymentioned; there are numerous applicationsofreceiver cathode ray'tubessuch as. H, Figure-1 ',.wherein the imagegenerated upon the fluorescent screen-1'6 is projected upon a screenandwherein the screen axis is ot normal to the optical axis of projection.With .such an arrangement,:.theimageupon the screenwill have 4 thescanning beam progresses from the top of the raster 23 to the bottomthereof.

In accordance with the principles of the present invention the keystonedraster 23 is obtained upon fluorescent screen [6 by the use ofconventional typelscanning signals app b dflection yoke 2H whichsignalsit'endito. producei'a rectangular raster, and by the use of twoopposed magnetic fields 25 and 26 having field lines which extendthrough the cathode ray tube II and are substantially perpendicular tothe axis of the tube and of theundeflecte'dzcathode ray beam andsubstantiallyl'paralleltoithe horizontal scanning lines of the raster233 Magnetic field filindicated by the plurality of crosses; Figure .1;isdisposed adjacent the fluorescent screen l6 and is directed into thepaper. The effect of a field so oriented is to uniformly deflect theelectron beam I5 upward as illustrated by the curvingloflthe'beam l5as-dt passes through-the field1region25. :If the beam-=l 5ordinarilwwould, trace 'outa rectangular patternon the-fluorescentscreenlfi then the altered-iangle.'of approaehlintroduced by field 2 5results-ins-a.keystonetraster sincethe path taken=by-thebeam 15 to:the-upper scanning lines-is longer than that (taken "tothe--lowerhorizontal scanning (lines.-

The fie1d-25, generated ibysmeans to[be herein-- after :describedis-preferably, a uniform fieldthat is; the lines either-field areessentiallyparal lel to each-otherand evenly distributedlas they.

traverse the-cathode raytube l In Furthermore' itl picture distortion;and is illustratedin- Figure 2. Thus,- the eflectof magnetic field: 25acting alone is to produce a substantially trapezoidal raster 23havingzsloping .sides, but wherein the horizontal: scanning; lines arebowed and fall tween \the limits of -curved, ..broken --lines 3! and. 32

Magnetic field 2e is.-disposed betweenttl' e :mas netic field 25 and thebeam -defiecting- -means' 2il and extends through the acathode ray tubein: a direction'or sense opposite-to field-25L It also is; a constantfield. As indicatedxby tile -plurality: of points-in Figure 1,.magnetic/field 26- is .substantially normal to and: directedout--ofg-rthepaper. It---willbe: apparent that the-ueffect of magnetic fieldlines 2 6- is to-direct the-scanning; electron .beaml5zdownwardasvindicated by thebeamcurvature in theregion-ofthe-lfield 25"; {soas tocompensate-forthe upward -defiection .eifect. of field 25. Inthis-manner, fields-25wand=2 acting together-produceno resultantdeflection :01'. the scanning pattern uponthe screen-- IS.

The magneticfieldgfi-is non-uniform; by which is meantthattthefield-lines-thereofl are-noLuniformly distributedand-.mutuallyiparallel. 'It -is' preferred thatthe magnetic fielddlibeestablishedl;by: two oppositearnagnetie poles. relativelyr com; centrated asdisclosed in connection with the aforementioned application of Fisherand John. Also as disclosed in this application, the non- A uniformfield 26 established by concentrated ophorizontal scanning lines, andthe amount of key stoning is dependent upon the amount by which field 25exceeds field 26. Generally, with conventional type receiver cathode raytubes, field 25 of the order of twice the strength of field 26. Thefinal trapezoidal pattern is, as illustrated in Figure 2, undistortedand centrally located upon the fluorescent screen l6. -'I 'he apparatusspecifically described includes a; cathode ray target which is fiat orslightly curved. This invention applies best to tubes with such screens,but it may be practiced to some advantage with tubes having other typesof screens. I

. The procedure for establishing the, required magnetic fields 25 and 26may be greatly varied. One embodiment of a magnetic structure capable ofproducing the required fields is illustrated in Figures 3A, B and C. Inthese figures, there is' dia'grammatically shown a cathode ray tube ll.as in Figures 1 and, 2. Figure 3A is a top view of the tube and magneticstructure. Figures 3B and'BC are side and front views of the tube andcorrespond with the views of Figures 1 and 2. The magnetic structurecomprises inexpensive means of obtaining the uniform strong field 25,and the non uniform comparatively weak field '26, and includes a pair ofcomparatively large, curved, soft steel pole faces 35 and 36 placedabout the screen end of the cathode ray tube H. A pair of magnets 31 and38 are placed adjacent the pole pieces 35 and 36 respectively and at anangle thereto.

{The magnets 31 and 38 are preferably permanent magnetsjalthoughelectromagnets may be used with equal efiect. As illustrated in Figure3Athe extended pole pieces 35 and 36, magnetized by the bar magnets 31 and38 establish the substantially'uniform magnetic field 25 adjacent thescreen of the tube. The free ends of'the magnets 31 and 38, that is,those ends not in contact with pole faces 35 and 36, establish thecomparatively weak and non-uniform field 26, located between the neck ofthe cathode ray tube and magnetic field 25.

Summarizing the above, a keystone compensation isobtained through theuse of a uniform magnetic field and a non-uniform magnetic field ofpredetermined strength, each generally substantially transverse to thecathode ray beam. The resultant scanning pattern is undisplaced upon thetube target screen. The strength of the uniform field is adjusted sothat there is no pattern displacement and the strength of thenon-uniform field is adjusted so that there is no horizontal linecurvature in the raster. If it is desiredto reverse the keystone effectillustrated in Figure 2, then the bar magnets illustrated in Figure-3may bereversed in polarity tojreverse the direction of the fields.

'l'teduced'to its elements, the principleunder- 6 lying the presentinvention is as follows. electron beam which may occupy any region of asquare pyramid, provided by the electron gun and the deflecting system,traverses a region occupied by a magnetic field '26, this field 26 acts.

on the beam to an extent depending on the in. tensity of the portion ofthe field traversed to introduce a keystoning of strength S1, adistortion D1 in the linearity of the scanning lines, and a displacementY, in the vertical position of the scanned area on the screen. Afterhaving left the region where the field 26 has a substantial effect, thebeam encounters a second .field 25, which also introduces similarefiects,which may be designated keystoning S2 distortion D2 anddisplacement .Y2. The fields have opposite senses, so that the neteffect on the screen is akeystoning of strength S2S1=So, a distortion ofextent D2D1=D0 and a displacement of extent Y2'Y1- Yo.

Inasmuch as the keystoning S varies with the.

tangent of the angle which the axis of the beampyramid makes with theundisplaced beam, the

distortion D varies with the barrelling or spread of the field, and thedisplacement Y varies with the tangent of the angle between the axis ofthe beam-pyramid and the undisplaced beam, as well as with the distancebetween the field, producing the displacement on the screen. The twofields 26 and 25, which are at different distances from the screen andof opposite senses may be combined to balance out the distortion D0 andthe displacement Yo, while leaving the desired amount of keystoning So.So will, of course, be less than S2. I

The above description and the figures are related specifically tokeystoning the image on a receiver type cathode ray tube. Theapplication of this magnetic keystone method to cameratype the receiverillustration above a trapezoidal image was required. It is furtherevident that there are various other magnetic andelectromagneticstructures which may be utilized to establish the properfields.

Since various modifications and extensions .of-

the principles hereinabove set forth may become evident to those skilledin the art, it is preferred that the spirit and scope of the inventionbe defined by the appended claims.

I claim:

1. In combination with a cathode ray tube having a fluorescent screen, amagnetic structure providing within said tube a plurality of continuousand fixed magnetic fields, one of said fields being of predetermineduniform configuration and being disposed adjacent said fluorescentscreen and the other field being of non-uniform configuration, saidfirst field producing a keystone effect at said screen with thehorizontal lines bowed and the second field producing a compensation forthe bowing of the horizontal lines.

2. In combination with a cathode ray tube, said tube having means-forgenerating an electron beam, means for deflecting said beam inaccordance with scanning signals and a fluorescent screen; a magneticstructure providing within said tube a plurality of continuous and fixedmagnetic fields, said fields being of predetermined uniform andnon-uniform configuration, said fields being disposed between saidcathode ray defiectingimea'ns andwsaid-fluorescent screemoner ofsaidifields producing; keystoning of-the -raster atisaidscreen withzthehorizontal lines bowed and the: other of said fields ofless-strengththan 'said first: field producing a compensation to.correct for said bowing. M

:3. llnicombinationiwithvacathode ray tube havingazmeansfor generatingan electron. beam,

means for deflecting saidf beam .in accordance.

withiscanning signals and: a fluorescent! screen; a magnetic structureprovidin -within "said tube. a plurality; of continuousiiandfixedimagnetic field's,

saidiifields being of predetermineduniform. and.

non-uniform configuratiomsaid fields beingydisposedzbetween said:cathode .ray 'defiectingime'ans and saidfiuorescent screen, one of said:fieldsiproducing'keystoning of the raster at said screen with'thehorizontal lines bowed and the other 'of said fields of less strengththan said first field means for deflecting said beam in accordance.

with scanning signals and a screen, means forcontrolling the keystoneeffect uponsaid screen comprising means for establishing two magneticfields of predetermined configuration within said cathode ray-tube andbetween a deflecting meansan'd said screen; oneof said fields beingin aplane transverse tothe axis of saidbeam and producing keystoning at saidscreen, the other of said fields being in a plane transverse to the axisof said beam and'in opposed direction to said first field.

5. In television apparatus, a cathode ray tube having means forgenerating an electron beam, means for deflecting said beam inaccordance with scanning signals and a screen, means for controlling thekeystone efiect uponsaid screen comprising means for establishin twomagnetic fields-oi predetermined configuration within said cathode raytube and between said deflecting means and said screen, one of saidfields being substantially uniform and the other'of said fields beingnon-uniform, said fields being substantially continuous andtfixed, oneof said fields being in a plane transverse to the axis of-said beamandiproducing keystoning'at said screen, the other of said fields beingin a plane transverse to the axis of said beam and in opposed-directionto said first field, and said other field compensating for bowingdistortion produced by said one of said fields.

6; In television apparatus, a cathode ray tube having means forgenerating an electron beam, means for deflecting said electron beam inaccordance with scanning signals and a target s'creen,.means forproducing a first magnetic field within said cathode ray tube andadjacent said target screen, said first magnetic field deflecting saidelectron beam at an angle to said screen, means for generating a secondmagnetic fieldadjacent said first mentioned deflecting means fordeflecting said electron beam at an angle to said screen andopposite tosaid first mentioned angle, whereby said first and second magneticfields providea keystone compensation upon said target screen.

7; In a television receiver, a cathode ray pictureftube having means forgenerating an electron beam, a fluorescent screen and meansfordeflecting said electron beam in accordance-with scanning signals to;provide. a scanning raster generating-av first rmagnetic :fieldwithinisaidi cathode ray tube: substantially parallel tOF SBid' afluorescent SOIJGBIIfiaTId adjaoentrthereto, means;

for generating-. a second magnetic: field: within: said cathode ray:tubeof opposite: direction relaw tive to said-first magnetic 'fieldiand disposed Lad jacent' to saidtdeflecting, means.

'8; In:atelevision receivenia cathode ray pic-' ture tubetiihavingimeans rforigenerating an :electron' beam, a: fluorescent screen? andmeans for deflecting said-electron beamsinzaccordance with scanningsignals: to: provide. 5 a scanning masters upon said: screen; Ime'ans;tori introducing-l azi-keystone: effect-r into: said raster I comprising'meansi for generating a first: magnetic flel'd w-ithin said-*- cathoderay tube substantially parallel ito s'aidt fluorescentscreen andadjacent 'thereto; means? for generating asecond magnetic field' withinsaid cathoderay tube of opposite "direction-"relie tive to said firstmagnetic-field anddisposed ad jacent to said deflecting means;- sa-i'd'fl'rst magnetic field being substantially uniform, I said sec-- ondmagnetic field being non-uniform.

9; In a television receiver, a cathoderay picture tube-having means-forgenerating an electrom beam, a fluorescent screen and means for" de-'fleeting said electronbeamdn accordance with scanning signals to providea scanning'raster upon-said screen, means for introducing a ke stoneeffect into said raster coniprisingmeans for generating a first magneticfield within said cathode ray tube substantially parallel to'saidfluorescent screen; and adjacent thereto; "means for generatinga'secondm'agneticfield within said cathode ray tube of oppositedirectionrel'ative' to said first magnetic field.and disposed adjacent?to said defi'ectingm'eans, saidfirst magnetic 'field' beingsubstantially uniform, said second. magnetic field being non-uniform,said means for' generating, said first] and second magnetic fieldcomprising a pair of oppositely, disposed. ,pfole pieces .ofmagneticlmat'erial. and a pair of. mag,- nets in contact with saidpolepieces.

10."Th'e method of deforming 'thelscanning; raster of a televisioncathode ray. tube I control keystoning which comprises theusteps ofestab-v lishing a first? uniform and continuous; magnetic. fieldextending through said" tube in one direc-. tion, and establishing asecond continuousuand: non-uniform magnetic field adjacent said. first;magneticifield and extending through said tube in .a direction opposite.tQ-said .fi'rst magnetic; field;

11'. In a television cathode ray. .tube ,having means for producingannelectroncbeam, means for directing said electronbeam ataefluorescentscreen, means for deflecting. said ,electronbeam in accordance with.horizontal andrvertical die.- flection scanning signals to produceaarasten .o horizontal scanning linesauponsaidl fluorescent screen, saidhorizontal scanning signals being of higherirequency than saidwerticalscanning sig nals, means for substantially uniformly varying: thelength, ofi said horizontal. scanning lines toprovide akeystone. effectcomprisingimeansifor establishing a first magnetic field havingwcontinuous and substantially uniform field lines through. said cathode raytube substantially, parallel to saidhorizo'ntallines, saidfirstmagneticfield being disposed adjacent to i said fluorescent screen, means foiestablishing.;a-second magnetic field having continuousand non-uniformr-fisld lines through said cathode ray tube and of opposite directionrelative to said first magnetic field lines, said second magnetic fieldbeing adjacent to said first magnetic field lines.

12. In a television cathode ray tube having means for producing anelectron beam, means for directing said electron beam at a fluorescentscreen, means for deflecting said electron beam in accordance withhorizontal and vertical deflection scanning signals to produce a rasterof horizontal scanning. lines upon said fluorescent screen, saidhorizontal scanning signals being of higher frequency than said verticalscanning signals, means for substantially uniformly varying the lengthof said horizontal scanning lines to provide a keystone effectcomprising means for establishing a first magnetic field havingcontinuous and substantially uniform field lines through said cathoderay tube substantially parallel to said horizontal lines, said firstmagnetic field being disposed adjacent to said fluorescent screen, meansfor establishing a second magnetic field having continuous andnon-uniform field lines through said cathode ray tube and of oppositedirection relative to said first magnetic field lines, said secondmagnetic field being adjacent to said first magnetic field lines, saidfirst and second magnetic fields acting to displace said raster inopposite directions, whereby substantially no resultant displacement ofsaid raster is obtained.

13. In a television cathode ray tube having means for producing anelectron beam, means for directing said electron beam at a fluorescentscreen, means for deflecting said electron beam in accordance withhorizontal and vertical deflection scanning signals to produce a rasterof horizontal scanning lines upon said fluorescent screen, saidhorizontal scanning signals being of higher frequency than said verticalscanning signals, means for substantially uniformly varying the lengthof said horizontal scanning lines to provide a keystone efiectcomprising means for establishing a first magnetic field havingcontinuous and substantially uniform field lines through said cathoderay tube substantially parallel to said horizontal lines, said firstmagnetic field being disposed adjacent to said fluorescent screen, meansfor establishing a second magnetic field having continuous andnon-uniform field lines through said cathode ray tube and of oppositedirection relative to said first magnetic field lines, said secondmagnetic field being adjacent to said first magnetic field lines, saidmeans for producing said first magnetic field including comparativelybroad field poles, said means for producing said second magnetic fieldincluding comparatively small field poles.

14. In a television cathode ray tube having means for producing anelectron beam, means for directing said electron beam at a fluorescentscreen, means for deflecting said electron beam in accordance withhorizontal and vertical deflection scanning signals to produce a rasterof horizontal scanning lines upon said fluorescent screen,

said horizontal scanning signals being of higher frequency than saidvertical scanning signals, means for substantialy uniformly varying thelength of said horizontal scanning lines to provide a keystone effectcomprising means for establishing a first magnetic field havingcontinuous and substantially uniform field lines through said cathoderay tube substantially parallel to said horizontal lines, said firstmagnetic field being disposed adjacent to said fluorescent screen, meansfor establishing a second magnetic field having continuous andnon-uniform field lines through said cathode ray tube and of oppositedirection relative to said first magnetic field lines, said secondmagnetic field being adjacent to said first magnetic field lines, saidmeans for producing said first and second magnetic fields comprising apair of comparatively broad magnetic pole pieces and a pair of permanentbar magnets in contact with said pole pieces.

15. In a television cathode ray tube having means for producing anelectron beam, means for directing said electron beam at a fluorescentscreen, means for deflecting said electron beam in accordance withhorizontal and vertical deflection scanning signals to produce a rasterof horizontal scanning lines upon said fluorescent screen, saidhorizontal scanning signals being of higher frequency than said verticalscanning signals, means for substantially uniformly varying the lengthof said horizontal scanning lines to provide a keystone effectcomprising means for establishing a first magnetic field havingcontinuous and substantially uniform field lines through said cathoderay tube substantially parallel to said horizontal lines, said firstmagnetic field being disposed adjacent to said fluorescent screen, meansfor estabishing a second magnetic field having continuous andnon-uniform field lines through said cathode ray tube and of oppositedirection relative to said first magnetic field lines, said secondmagnetic field being adjacent to said first magnetic field lines, saidmeans for producing said first magnetic field including comparativelybroad field poles, said means for producing said second magnetic fieldincluding comparatively small field poles, said uniform field beingsubstantially stronger than said non-uniform field.

WILLIAM E. BRADLEY.

REFERENCES CITED The following references are of record in'the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,177,688 Cawein Oct. 31, 19392,227,711 Gunther Jan. 7, 1941 2,255,039 Gunther Sept. 9, 1941 2,258,643Degier et a1 Oct. 14, 1941 2,259,233 Tingley Oct. 14, 1941 2,264,567Gunther Dec. 2, 1941 2,297,407 Gunther Sept. 29, 1942

